The present invention relates to computer systems, and in particular to computer systems having processing units, which are connectable to a communications network via which information may be communicated.
There are many fields in which mankind has become reliant on computers to perform valuable and sometimes essential functions. The reliance on computer systems demands that the downtime of a computer system is as short as possible. The downtime of a computer system is a period during which a computer system is inoperable, for example as a result of a fault in the system. If a computer system goes down, the inconvenience and loss of revenue caused can be substantial. For example, if a computer system is operating as a server or exchange forming part of a telecommunications system, then during the down-time no communications can be performed using the telecommunications system, which can result in a considerable loss of business and therefore revenue for an organization. Computer systems are therefore arranged to be as reliable as possible, so that the downtime is reduced to a minimum. Accordingly, the up-time of a computer system may be required to be in the order of 99.9995%, which equates approximately to a down-time of a few seconds per year.
Computer systems are designed and manufactured to standards that reduce as far as possible the likelihood of malfunction. However, in order to minimize any down-time, which may occur as a result of a malfunction, it has been proposed to design parts of the computer system such that a part can be replaced as quickly as possible with a part which performs the same function.
In this context, a processing unit of a computer system can be arranged to be replaceable. The computer system can include one or more processing units interconnected via a network. The processing units are connectable to the network and can include one or more processors and a hard disk drive or other storage device containing software that controls the operation of the processing unit. Alternatively, or in addition, the processing unit can include a preprogrammed controller or microcontroller for providing processing functions. The processing unit typically also includes other components mounted on one or more carriers, for example on a motherboard. The processing unit often is housed in an enclosure, but may also be configured as a motherboard without a housing that plugs into a backplane.
Particularly in systems comprising multiple processors interconnected by a network for use in a telecommunications environment, the processors are configured as field replaceable units (FRUs) that are designed to be replaced in the event of a malfunction occurring in the processing unit. In such a situation, the hard disk of the replacement processing unit is often provided with pre-loaded software equivalent to the software processes loaded onto the original hard disk. The original processing unit may then be repaired off-line.
Such pre-loaded software, while equivalent to the software loaded onto the original hard disk, requires input of configuration information to cause the replacement FRU to be able to function as the original FRU. Such configuration information is traditionally stored on a mounted filesystem (i.e. the local hard disk) and therefore needs to be moved to the new FRU. Moving hardware such as disks from one FRU to another is time-consuming and risks damaging the hardware. Also, the disk of the failed FRU may be the component of that FRU responsible for the failure. Further, many FRUs are provided as “sealed” units configured not to allow components thereof to be extracted and replaced in the field. In order to move this configuration information without swapping the disk requires changes to be made to each application and user intervention in the event of failure.
The processing unit can also include communication interfaces to enable connection to a communications network. This can be used to effect communication between different parts of a computer system, which computer system includes the processing unit, and/or between different computer systems. The communications network concerned can, for example, be a local bus, a local area network, an intranet or the Internet or the like. In order to communicate via a network, the processing unit needs to be able to identify itself to the network. It is therefore provided with a network identity.
For example, communications networks, operable under an Ethernet protocol or the like, communicate data via a common medium to processing units attached to the medium by appending the data to network identities which the processing units recognize. Each processing unit which is arranged to communicate using a particular network standard such as Ethernet is therefore provided with a unique address, so that the processing unit may communicate via any network conforming to that standard. Typically, processing units forming part of a computer system are provided with a communications interface such an Ethernet interface, for embodying the network identity. Once the processing unit has been connected to the communications network, the network identity for that processing unit will be used by all other processing units connected to the communications network. This is typically arranged in that the processing units themselves receive, or a separate processing unit receives, the network identities from other processing units and pass(es) the network identities via a so-called device tree and they are then stored so as to provide configuration information to enable communication via the network.
Accordingly, processing units arranged to communicate via a communications network are each provided with a network identity, which is generally stored in memory of the processing unit. If a processing unit is replaced by another processing unit, the communications network and the devices connected to the communications network will not recognise that processing unit and so will be unable to communicate with the processing unit.
In order to effect replacement of a processing unit, the replacement processing unit should be arranged to communicate via the communications network, in substantially the same way as the original processing unit communicated and be configured to operate in substantially the same way as the original processing unit operated. In order to minimize downtime, it is desirable that the replacement be made as quickly and efficiently as possible.